Quick answer
Cubic yards of concrete for a slab, plus bag counts. Enter length, width and depth / thickness and the concrete calculator returns cubic yards, cubic feet and cubic metres.
Related tools: Cubic Yards Calculator: Cubic yards, cubic feet and cubic meters from length, width and height. Gravel Calculator: Cubic yards of gravel for an area. Mulch Calculator: Cubic yards of mulch for a bed.
How to use the Concrete Calculator
- Enter length (ft) (above 0).
- Enter width (ft) (above 0).
- Enter depth / thickness (in) (above 0).
- Optionally, enter waste allowance (%) (between 0 and 50). It starts at 0.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Length | A number, in ft | > 0 |
| Width | A number, in ft | > 0 |
| Depth / thickness | A number, in in | > 0 |
| Waste allowance (optional) | A number, in % | ≥ 0, ≤ 50, starts at 0 |
Formula and method
Formula
cubic yards = length (ft) × width (ft) × depth (in ÷ 12) ÷ 27
IEEE-754 double precision; shown to at most 6 decimal places.
27 ft³ = 1 yd³. A waste allowance is added to the total. Bag counts use manufacturer yields of 0.60 ft³ per 80 lb bag and 0.45 ft³ per 60 lb bag of ready-mix concrete; check your product's label.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Length = 10; Width = 10; Depth / thickness = 4.
| Result | Value |
|---|---|
| Cubic yards | 1.2346 yd³ |
| Cubic feet | 33.3333 |
| Cubic metres | 0.9439 |
| 80 lb bags | 56 |
| 60 lb bags | 75 |
Example 2
Inputs: Length = 10; Width = 10; Depth / thickness = 4; Waste allowance = 10.
| Result | Value |
|---|---|
| Cubic yards | 1.358 yd³ |
| Cubic feet | 36.6667 |
| Cubic metres | 1.0383 |
| 80 lb bags | 62 |
| 60 lb bags | 82 |
The first line is the headline result (cubic yards). Below it the concrete Calculator lists cubic feet, cubic metres, 80 lb bags and 60 lb bags, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Planning a slab
Residential slabs for patios and walks are commonly poured about 4 inches thick, and heavier loads call for more thickness and reinforcement. Follow your local building code and ask a qualified professional for structural work.
This calculator adds a waste allowance because forms are never perfectly level and some concrete is lost in mixing and placing. It also converts the volume to bags using the yields printed on bagged mix: 0.60 cubic feet per 80 lb bag and 0.45 cubic feet per 60 lb bag. Check the label of your product, because yields vary.
Concrete for a 10 ft × 10 ft slab at different thicknesses
Every figure in this table comes from running this calculator, so it matches what the form returns.
| Thickness (inches) | Cubic yards | 80 lb bags |
|---|---|---|
| 4 | 1.2346 | 56 |
| 5 | 1.5432 | 70 |
| 6 | 1.8519 | 84 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Depth / thickness: entering "0" shows "Depth / thickness must be greater than 0." beside that field and no result.
Choosing between the Concrete Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Cubic Yards Calculator](/construction/cubic-yards-calculator/) | length, width and height or depth | Volume |
| [Gravel Calculator](/construction/gravel-calculator/) | length, width and depth / thickness | Cubic yards |
| [Mulch Calculator](/construction/mulch-calculator/) | length, width and depth / thickness | Cubic yards |
| [Square Footage Calculator](/construction/square-footage-calculator/) | length, width and unit | Area |
| [Soil Calculator](/construction/soil-calculator/) | length, width and depth / thickness | Cubic yards |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Rectangular volume only
- Round up when ordering
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for depth / thickness to confirm this.
Frequently asked questions
What does the Concrete Calculator calculate?
Cubic yards of concrete for a slab, plus bag counts. It returns Cubic yards, Cubic feet, Cubic metres, 80 lb bags and 60 lb bags.
What formula does the Concrete Calculator use?
cubic yards = length (ft) × width (ft) × depth (in ÷ 12) ÷ 27. 27 ft³ = 1 yd³.
What do I need to enter in the concrete Calculator?
You enter Length (ft), Width (ft) and Depth / thickness (in). Optional: Waste allowance (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Rectangular volume only.
What are the limits of this calculator?
Rectangular volume only. Round up when ordering.
What is an example of a concrete result?
With length 10, width 10 and depth / thickness 4, the cubic yards is 1.2346 yd³.
Where does the method come from?
The method follows: Manufacturer yield figures for 60 lb and 80 lb pre-mixed concrete bags (Quikrete product data).
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Rectangular volume only.
Related calculators
- Cubic Yards Calculator — Cubic yards, cubic feet and cubic meters from length, width and height.
- Gravel Calculator — Cubic yards of gravel for an area.
- Mulch Calculator — Cubic yards of mulch for a bed.
- Square Footage Calculator — Area of a rectangular space in square feet, square metres and square yards.
- Soil Calculator — Cubic yards of soil for an area.
- Sand Calculator — Cubic yards of sand for an area.
- Concrete Weight Calculator — Weight of a volume of concrete from its density.
- Concrete Mix Calculator — Cement, sand and aggregate for a nominal volume mix such as 1:2:4.
- Paint Calculator — Gallons of paint for the walls of a room.
Sources
- Manufacturer yield figures for 60 lb and 80 lb pre-mixed concrete bags (Quikrete product data)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.